The present invention relates to a process for conducting reactions which are characterized by an equilibrium.
1. Field of the Invention
Numerous chemical reactions including such reactions which are conducted in an industrial scale are characterized by the fact that a chemical equilibrium between educts and products is reached after a certain reaction time, which equilibrium may prevent the course of the chemical reaction from largely running to generate the desired products and, hence, may also prevent a high yield of the desired products from being obtained which high yield is important for the commercial value of said reaction.
2. Discussion of the Background
There are various attempts to solve such a problem by trying to influence the equilibrium of a chemical reaction in the desired direction. The basis for such attempts is the so-called mass action law (xe2x80x9cMassenwirkungsgesetzxe2x80x9d) and the equilibrium constants which are dependent upon the reaction conditions and are defined by said law. Following the Le Chatelier principle, the chemical reaction runs into the desired direction, and there is established a new equilibrium which, due to a suitable influence, is shifted more to the side of the products.
Examples for such equilibrium reactions are the esterification of a carboxylic acid with an alcohol, resulting into the generation of an alklester of said carboxylic acid and water in accordance with the following equation:
R1COxe2x80x94OH+R2Oxe2x80x94H≈R1COxe2x80x94OR2+H2Oxe2x80x83xe2x80x83(1)
By continuously distilling off the water generated in the course of the reaction or by feeding the educts (carboxylic acid or alcohol) in excess, the equilibrium is shifted towards the right product) side of the above equation. In a comparable manner, carboxylic acid alkyl esters may be transesterfied in the presence of alcohols and will set free the alcohol of the alkoxy group formerly bound in the starting ester:
R3COxe2x80x94OR4+R5Oxe2x80x94H≈R3COxe2x80x94OR5+R4Oxe2x80x94Hxe2x80x83xe2x80x83(2)
A change of the reaction conditions (temperature, pressure) may contribute to influencing the state of the equilibrium, too. Practically, the above-mentioned measures for shifting the equilibrium to the product side do not always result into the desired success. Usually, this is due to the fact that a change of the reaction conditions is also accompanied by the generation of by-products which may raise problems not only in view of the product yield but also in view of the purity of the products. Separating undesired by-products from the desired products may strongly adversely affect the economic efficiencyxe2x80x94particularly in a big-scale production. The presence of large amounts of educts or starting materials initially fed in excess amounts often results into problems in connection with the purification of the desired product.
Physical equilibria may play a role, too, in conducting chemical reactions,
It is, for example, often required that certain reactions are conducted in (for example liquid) media which are free of oxygen or water or humidity, respectively, physically dissolved in the medium provided for a reaction. Usually, the air is exhausted from the vessel containing the medium in such a case, and the vessel is filled with an inert gas subsequently. Alternatively, the open system is rinsed or flushed, respectively, with an inert gas for a certain time. By such steps, the undesired gas or the humidity is stripped from the system; however, the inert filling gas or rinsing gas is lost. In addition, in plants for technically conducting chemical reactions, such steps cannot be carried out economically.
Solution equilibria of chemical substances in solutions may play in important role in conducting chemical reactions in a large scale, too. Subsequent to a chemical reaction, undesired by-products or educts may be dissolved in the reaction mixture. By-products as, for example, colouring agents or odoriferous substances or low-molecular by-products of a reaction randomly resulting into higher-molecular products or, in a similar manner, non-reacted educts remaining in the reaction mixture will have to be removed in costly purification steps which usually remarkably decrease the product yield.
The solution equilibriaxe2x80x94in these cases: diffusion-determined solution equilibriaxe2x80x94also include equilibria for dissolving gaseous reactants in liquid reaction systems. In the course of reactions including a gaseous and a liquid phase as, for example, hydrogenation reactions, oxidation reactions, nitrilation reactions, phosgenation reactions or alkoxylation reactions with alkylene oxides, the reaction rate, i. e. the rate by which an equilibrium is established which is shifted to the right (product) side as far as possible, is determined mainly by the amount of gas available in the liquid reaction medium for a contact with a dissolved reactant. For achieving practically useful reaction rates in usual reactions, the partial pressure of the reaction gas had to be relatively high in order to secure a sufficient gas concentration. This fact not only made a control of the reaction difficult sometimes, but, under usual conditions, also required the input of larger gas amounts than actually necessary for the reaction. Moreover, at the end of the reaction, it could not be avoided that a certain amount of unreacted gas had to be removed, since the partial pressure of said gas in the gas space was not sufficient for completely terminating the reaction of the gaseous reactant in said liquid reaction medium within an acceptable reaction time. The latter situation is not acceptable particularly in a case where the gas cannot be exhausted into the environment for safety reasons but has to be disposed expensively. This requirement, too, decreased the economic efficiency of many gas-liquid reactions considerably.
The invention had as an object to remove the above-described disadvantages of the prior art. In particular, there should be provided a process for conducting chemical reactions which are characterized by an equilibrium where the step of influencing the equilibrium, in favour of the desired course of the reaction, is possible to be taken in a simple and efficient way and by using means which do not put up physical or chemical resistance to a shift of the equilibrium.
It was a further object of the invention to provide such a process wherein the means for shifting the equilibrium is applicable as broadly as possible. Hence, the means should be inert to chemical reactions and, in view of economically conducting the process, should be cheap and available everywhere.
Further objects, advantages, and features of the process according to the invention may be learnt from the following description.
Surprisingly, it was found that it is possible to circulate, in a process of conducting chemical reactions which are characterized by an equilibrium, an inert gas in a separate gas loop, whereby it is possible to achieve the above-described objects.
The invention relates to a process for conducting a chemical reaction characterized by an equilibrium in a reaction system designed as a loop reactor, said loop reactor comprising a reactor vessel, at least one loop connected to said reactor vessel each by means of an outlet and an inlet, said loop comprising means for pumping over a fluid reaction material, at least one heat exchanger, optionally means for feeding said reaction material into the reactor vessel and a separate gas loop which is connected to the gas space of the reactor vessel above the reaction mixture and has separate means for feeding a gas into the gas loop, for withdrawing gas from the gas loop and/or for treating said gas circulating in the gas loop, said process comprising the steps of circulating and/or treating said gas in said gas loop, feeding said gas into the reactor vessel for influencing the equilibrium of a reaction conducted in said reactor vessel and being characterized by the equilibrium and, after influencing said equilibrium reaction conducted in said reactor vessel, exhausting said gas from said reactor vessel into the gas loop.